This invention relates to a vacuum packaging method and apparatus for packaging relatively large foodstuffs such as livestock meat and block cheese or other articles with indeterminate shapes through the use of packaging bags of a heat-shrinkable plastic film (thermoplastic film) in a vacuum environment.
It is well known to package foodstuffs such as livestock meat with thermoplastic packaging bags in a vacuum environment. For this purpose, the foodstuffs to be packaged are supplied into a plurality of vacuum chambers disposed on the periphery of a turntable. This typee of a vacuum packaging apparatus is called a rotary chamber type. Some of this type of apparatuses are disclosed in U.S. Pat. Nos. 2,630,955, 2,740,243 and 3,598,391.
In these apparatuses, eight vacuum chambers are disposed at equal space intervals on the periphery of a turntable which is rotated at a constant speed. At an angular position of the turntable, a packaging bag containing an article therein in a state wherein one end of the packaging bag is open is supplied onto a support plate of a vacuum chamber. After the support plate receives the packaging bag, the vacuum chamber is closed to make a vacuum therein (vacuum process) and then the opening of the packaging bag is sealed by a heated seal bar disposed in the vacuum chamber (sealing process). The sealed portion of the packaging bag is cooled down for some seconds in a state wherein the sealed portion is held by the sealed bar and a pillow head located on the support plate. After the completion of the sealing process, the vacuum chamber is opened to discharge the packaged bag and thereafter an article to be packaged is fed onto the support plate (bag loading and unloading process). In this manner, a new packaging bag is packaged in a vacuum environment during one rotation of the vacuum chamber and the three processes need a certain period of time, that is, each of the processes needs a certain angular range of the turntable, respectively.
Furthermore, in these packaging apparatuses, the turntable is normally rotated at almost the maximum speed in order to increase packaging efficiency. Even if the number of the vacuum chambers is decreased to four in order to make a packaging apparatus small, each process needs a certain period of time and the period cannot be shortened easily. Accordingly, it is not possible to make a packaging apparatus compact or light in weight while maintaining a certain speed suitable for processing the packaging bags efficiently.